1. Field of the Invention
The present invention relates to a control apparatus for controlling relative movement between a tool and a workpiece on a machine tool in accordance with a numerical control program.
2. Description of the Prior Art
In a numerical control machine tool, a workpiece can be precisely machined to a desired dimension in so far as a numerical control program is input correctly. However, when one of a plurality of portions to be machined of a workpiece is not machined to a desired dimension due to errors in inputting numerical control data, said one portion has to be remachined subsequently.
In this case, an attempt may be made to revise a part of the numerical control program which causes an undesired dimension at the one portion of the workpiece and then, to perform the machining operation again in accordance with the revised numerical control program. However, such an attempt may results in that desirably finished portions of the workpiece which do not require remachinings are damaged to have, for example, scratches by the contact with a machining tool. To avoid this problem, in a known machine tool, the operational mode is switched from an automatic mode to an individual mode, and a manual pulse generator is then manipulated to move a tool in such a manner as to remachine a portion of the workpiece which has not been machined to a desired dimension.
In the known machine tool of the type mentioned above, since the remachining of the workpiece is performed by moving the tool by the manipulation of the manual pulse generator, it is possible to remachine those portions which can be machined by moving the tool along one control axis at a time, but impossible to remachine precisely those portions such as arcs, tapered surfaces and so forth which cannot be precisely machined in a manner other than the simultaneous distribution of pulses to two control axes.